Lubricating oil



Patented Dec, 3i, i940 s'rATEs LUBRICATING OIL Harry V. Ashblirn and BobcrtEConai-y, Beacon, and Paul S, Stutsman, Fishkill, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application March 16, 1939, Serial No. 262,198

'7 Claims.

This invention relates to a lubricating oil, and particularly to a motor oil adapted for lubrication of the bearings and cylinders of internal combustion engines, such as automotive engines, airplane engines, Diesel engines, andthe like.

The modern development of internal combustion engines with extremely small clearance between piston and cylinder wall, together with the modern development of highly solvent refined lubricating oils for use in the crankcases of such engines, has given rise to the problem of so-called varnish or lacquer formation. This varnish generally appears as a yellowish or reddish brown film which deposits upon the metal surfaces, including the piston rings and skirt, and cylinder wall during operation of the engine over extended periods of time. In the newest engines having extremely small clearances and high compression, the building up of this varnish film increases the frictional resistance to the reciprocation of the pistons, thereby raising fuel consumption and reducing power output; and this deposit may become so severe as to frequently result in seizure of the pistons when the motor is stopped and allowed to cool.

Further, the modern development of the highly refined motor oils together with the modern development of the new type bearings, including the connecting rod and main bearings of internal 30 combustion engines, which has involved a departture from the old babbitt bearings and has given rise to the new alloy bearings of the type of cadmium-silver copper-lead, cadmium-nickel and the like, has also presented the industry with the 35 problem of bearing corrosion.

The majority of straight uncompounded refined lubricating oils on the market today are found to result in substantial varnish deposition 40 and bearing corrosion when used as crankcase lubricants in these new type engines.

It is an object of the present invention to provide a lubricating oil which is effective to inhibit this varnish formation and bearing corrosion.

It is a further object 01. this invention to provide such a lubricating oil in which the additive is of such character as not objectionably to affect, but even to improve, other desirable properties and tests of the motor oil, particularly stability in storage and service, resistance to oxidation and sludge formation, demulsibility, reduction in oil ring and compression groove deposits with prevention of ring sticking and reduction in piston and cylinder wear.

We have discovered that a mineral lubricating 55 oil of the motor oil type, such as a modern highly solvent refined lubricating oil, can be converted 60 to of a small proportion o1 an oi1-soluble alicyclic organic phosphite compound having the general formula in which A is an alicyclic organic radical of the type r RR R R c sis! in which R represents hydrogen or the same or different alkyl, aryl or aralkyl radicals, and in which R1 and R2 above represent hydrogen or the same or different alicyclic radicals or the type enumerated for A above. By aiicyclic phosphite compounds, it is understood that this means the phosphitev estersoi that group of cyclic organic compounds derived from the corresponding acyclic compounds, such as the cycloparaflins or the formula CGHII, in which the alicyclic radical is substituted for one or more of the hydrogens of phosphorous acid giving the corresponding mono-, dior tri-phosphite.

As representative of compounds oi this group which has been found highly efl'ective tor purposes of this invention, there is mentioned triwhich may be written (CaHnlsPOs, in which three cyclohexyl radicals are substituted for the three hydrogen atoms of phosphorous sold. Similar diand mono-cyclohexyl phosphite compounds are also included, such as di-cyclohexyl mono-hydrogen phosphite and mono-cyclohexyl di-hydrogen phosphite. Similarly, the mono-, dior tri-alkyl substituted cyclohexyl phosphite compounds are included, such as those containing the corresponding substituted radicals oi methyl-cyclohexane, 1,1-di-methyl-cyclohexane, 1,2- dimethyl cyclohexane, 1,3-dimethyl cyclohexane, 1,4-dimethyl cyclohexane, ethyl cyclohexane, 1,2-methyl ethyl cyclohexane, normal propyl-cyclohexane, 1,3,S-trImethyI-cyclohexane, 1,3,4 trimethyl cyclohexane, 1,3,5 dimethyl ethyl-cyclohexane, 1,4-mcthyl lsopropyl cyclo lid hexane, and the like. Likewise, similar phosphite compounds containing the aryl or aralkyl substituted cyclohexyl radical or radicals are contemplated, including those in which one or more of the hydrogens of a substituted cyclohexyl radical or radicals is substituted by phenyl, tolyl, xylyl and the like.

These alicyclic phosphite compounds and their method of preparation are disclosed and claimed in the co-pending application of Robert E. Conary and Harry V. Ashburn, Serial No. 262,199, filed concurrently herewith. For purposes of illustration, this invention is described in connection with the use as an additive of tri-cyclo hexyl-phosphite, although it is to be understood that the invention is not limited thereto. This particular compound was prepared by the addition of one mol of phosphorus trichloride to three mols of dry cyclohexanol, an excess equivalent to approximately 3.3 mols of dry pyridine and approximately an equal weight of dry benzene being present. The phosphorus trichloride was added dropwise to the mix of cyclohexanol, pyridine and benzene, with adequate stirring while the temperature was held at about 23-50 F'. After complete addition of the phosphorus trichloride, the mixture was allowed to warm up to room temperature, then heated to boiling and refluxed for about two hours. After cooling to room temperature, the mixture was washed with cold water until the wash water gave no acid test to litmus. The mixture was then dried over anhydrous sodium or calcium sulfate, the remaining pyridine, benzene and unreacted cyclohexanol removed by distillation under vacuum, and the desired product was obtained by vacuum distillation, passing over at approximately 329-347 F. under an absolute pressure of about 10-15 mm. mercury. The material was an oily liquid soluble in lubricating oil and insoluble in water. From constituent analysis and particularly phosphorus content, the said material was primarily tri-cyclohexyl phosphite mixed with a minor proportion of di-cyclohexyl phosphite in the ratio of approximately 80-90% of the triester to 20-10% of the dl-ester.

The additive is added to the mineral lubricating oil in a proportion of about 0.01-2.0% by weight, and preferably of the order of 0.25-0.5% by weight. The material dissolves readily in the lubricating oil at room temperature with agitation, but its solution may be facilitated by heating the oil mildly. It apparently forms a stable solution which is not subject to separation, precipitation or sedimentation in storage or under service conditions, and is not volatilized or lost in service conditions normally encountered in crankcase lubrication.

A rigorous test which is used to determine the effectiveness of additives to stabilize lubricating oils of this type against oxidation and inhibit varnish formation and bearing corrosion is the so-oalled catalyzed Underwood oxidation test, which is described in a pamphlet dated August 1, 1938, of the Research Laboratories Division of the General Motors Corporation entitled Underwood oxidation testing apparatus. This test briefly consists in abrading the inside or concave surface of half of a standard cadmiumsilver automotive bearing by a motor-driven wheel covered with abrasive cloth until an evenly scratched surface is obtained. A copper strip 10 inches long by 2 inches wide is also abraded by sanding until an evenly scratched surface is obtained. The strip and bearing are cleaned by washing in solvent (a mixture of equal parts of denatured ethyl alcohol, toluol, and ethyl acetate), dried and weighed. The copper strip and. bearing are then immersed in the oil to be tested in a box or trough equipped with pump recirculation for continuously circulating the oil over the bearing and strip, the apparatus having previously been carefully cleaned. The recirculating oil is heated to a temperature of about 325 F. and maintained at this temperature during the period of test of fifteen hours. A small proportion of the order of 0.01% of iron oxide added as iron naphthenate is added to the oil undergoing the test in order to catalyze the oxidation and bearing corrosion, and to more closely simulate the conditions encountered in crankcase lubrication where the oil is in contact with iron.

A sample of the oil undergoing test is withdrawn at five-hour intervals, and likewise the bearing and copper strip are removed at fivehour intervals, carefully cleaned and weighed and again re-immersed in the oil bath. At the conclusion of the fifteen-hour run, the copper strip is removed, soaked for about ten minutes in precipitation naphtha to remove adhering oil, dried and weighed. The increase in weight is recorded as weight of varnish accumulation. The test bearing is likewise removed, carefully cleaned with solvent which is effective to remove both oil and the varnish film, dried and weighed, and the loss in weight is recorded as bearing weight loss. The samples of oil from the two intermediate five-hour periods and from the end of the run are tested for Saybolt-Universal viscosity at 130 F., neutralization number, Conradson carbon residue, material insoluble in A. S. T. M. precipitation naphtha (expressed in mg. per ten grams of oil), and chloroform-soluble portion of the naphtha-insoluble residue (expressed in mg. per ten grams of oil). The above test is run first with the blank oil, then with the same blank oil containing the desired proportion of the additive, and a final run is again made with the blank oil. The results of the two blank runs may be averaged or may be reported separately in comparison with the results of the compounded oil.

The following are the results of a catalyzed Underwood oxidation test on a furfural refined dewaxed Mid-Continent distillate lubricating oil of S. A. E. 10 grade and the same oil containing 0.25% of the cyclohexyl phosphite prepared as set forth above:

B] k 33 5; Bl k an an 'lest oil cycloliexyl oil phosphite Percent iron oxide added as iron naphthenate 0.01 0.01 0. 01 Neutralization number, 16 hours... 45.0 3. 76 14.0 Bearing corrosion, grams, 5 hours... 0. 434 0.028 0.376 Bearing corrosion, grams, hours.. 0.865 0.032 0. 772 Bearing corrosion, grams. 16 hours. 1. 488 0. 032 l. 137 Naphtha-insoluble ercent, hours 13.03 0.83 16. 24 Ch oroform solu le percent. 15

hours 12.05 0. 66 13. 65 Conradson carbon percent, 15 hours. 6. 44 0. 97 5. 33 S. U. viscosity at 130 F., init1a1. 94. 5 94. 5 94.5 S. U. viscosity at 130 F., 15 hours.. 1700 141. 5 4000 Percent increase in viscosity. 1800 49. 8 4140 Copper loss, m g 69 5 324 Varnish deposit, mg 42 30 160 The above tests indicate very pronounced superiority of the compounded oil over the blank oil with respect to bearing corrosion as shown by the bearing corrosion and copper loss tests, with re-* spect to oxidation stability as shown by the neutralization number, naphtha-insoluble. chloroform soluble, Conradson carbon and viscosity tests, and with respect to inhibiting varnish deposit as shown by the varnish deposit and chloroform-soluble tests.

Practical tests in an actual automotive engine confirmed the superiority of the compounded oil of the present invention in inhibiting varnish deposit. This test was run in a standard Chevrolet engine operated on a block for thirty hours at an equivalent of fifty miles per hour or 1500 miles, with a crankcase'temperature of about 290 F. for an S. A. E. 20 oil and about 275 F. for an S. A. E. 10 oil, with a jacket temperature of 212 F. and crankcase ventilation of 'one cubic foot per minute. A series of tests were run on the same engine under these conditions using for crankcase lubrication a furfural-refined dewaxed Mid- Continent distillate lubricating oil of S. A. E. 20 grade in comparison with the same oil containing a small proportion of an additive heretofore known to us as being very effective for varnish deposit inhibition andtermed herein for purposes of description a compounded S. A. E. 20 oil; and another series of tests were run on ,a furfuralrefined dewaxed Mid-Continent distillate lubricating oil of S. A. E. grade 10 containing the same proportion of said last mentioned additive, and termed herein for purposes of description a compounded S. A. E. 10 oil, .in comparison with the same S. A. E. 10 oil (uncompounded) to which was added 0.25% of cyclohexyl phosphite prepared as outlined above. At the completion of each run, the engine was taken down, the pistons removed and the varnish deposit determined on the oil rings and the piston skirt. This was accomplished in each case by washing first with precipitation naphtha to remove retained oil,

then washing with acetone to remove the acetonesoluble portion of the varnish which is found to represent the bulk of the varnish deposit, then evaporating this acetone solution to dryness. extracting the residue with precipitation naphtha to remo-veremaining traces of oil, again taking up in acetone solution and filtering to remove suspended carbon particles and impurities, and finally evaporating the acetone solution to dryness. The weight of the residue is expressed as mg. of varnish deposit for the piston skirt and the oil rings respectively. The following results were obtained:

In explanation, it may be stated that a lighter A lubricating oil of the motor oil range tends to show greater varnish deposit than a heavier oil of the same character, as is shown by the tests on the compounded S. A. E. 20 oil and the compounded S. A. E. 10 oil above. These tests show that the compounded oil is greatly superior to the uncompounded oil, and further show that the cyclohexyl phosphite of the present invention is markedly better than the previously known additive which was employed in the compounded oil rtests for purposesof comparison. The unusual eiiectiveness of the additivesof F. by an external heat exchanger with external pump, and with. a water jacket temperature of 212 F'. The bearings prior to each run were carefully weighed, and then assembled, the run carried out and the bearings disassembled, carefully cleaned and again weighed, the bearing corrosion being expressed as weight loss in grams.

The following tests were made in this manner comparing an uncompounded furfural refined clewaxed Mid-Continent distillate lubricating oil of S. A. E. 40 grade with thesame oil containing of cyclohexyl phosphite prepared as outlined above:

Oil tested Weight loss,

grams Blank S. A. E. 40 oil Blank S A. E. 40 oil plus 0.25 percent cyclohexyl phosphite 0. 338

Blank S. A. E. 40 oil .n. 1 l3. 9

In addition to the advantages enumerated above, it is found that the alicyclic phosphites of the present invention can be added to high grade typical motor oils without objectionably aifecting desirable properties or tests of these oils as illustrated in the following table, setting forth tests on a furfural-refined dewaxed Mid-Continent distillate lubricating oil of s. an. 30 grade in comparison with the same oil containing 0.25% cyclohexyl phosphite:

Reerence Same reference 30 grade phosphite A. P. I. gravity 28.3 28.1 C. 0. flash, "F 460 460 Fire 525 535 s. U viscosity at "F 497 501 S. U. viscosity at "10 F 62 62 Color-Lovibond 6 240 255 Conradson carbon residue, percent. 0. 09 0. i4 Pour, F -5 -5 Cloud, F 0 -2 0. 04 0. 04 0. 6 1. 2 0. 004 0.02

compounded oils of the present invention also meet the Navy Emulsion Test, as determined by the United States Government test No. 320.12 as found on pages 76 et seq. oi appendix 6 "Lubrlcants and liquid fuels" issued by the Navy Department August 1, 1928, with specifications set forth on page 7 of Naval Engineering Bulletin 31 "Lubricating on" published by the United States Government Printing Ofllce in 1937. Briefly, these specifications require that an emulsion of lubricating oil having a Saybolt-Universal viscosity at 210 F. in excess or fifty-five seconds with water at 180 F. or with a 1% NaCl solution at 180 F. shall break in The following tests indicate the effectiveness of less than sixty minutes.

the above noted reference S. A. E. 30 cmpounded with 0.25% cyclohexyl phosphite in meeting these specifications in comparison with the uncompounded reference oil:

Water emulsion test Reference Reference S. A. E. 30

E. 30 oil+O.25%

oil e3 elohexyl pliosphite Ceoilscporntcd, l5miuutes. I 40 40 Ce. water separated, minute iii) 40 (.c. emulsion left. 15 minutesv l 0 Time of complete separation, in minutes. it) 7 1% NaCl solution emulsion test The use of certain aryl and alkyl phosphites, such as triphenyl phosphite and tributyl phosphite, in motor oils of this character has previously been suggested for the purpose of reducing bearing corrosion. While these materials display some effectiveness for this purpose, they are not particularly effective for inhibiting oxidation as determined by the catalyzed Underwood Oxidation Test. On the other hand, the compounds of the present invention are found to possess the unusual and unexpected property of combining in one material the ability to inhibit bearing corrosion, varnish deposit and oxidation of a lubrieating oil in which they are used, and to do this in a greatly superior manner.

Obviouslymany modifications and variations of the invention as hereinbeiore set forth may be made without departing from the spirit and scope thereof, and only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method of lubricating bearing surfaces of 50 an internal combustion engine, which comprises aaaasaa maintaining between the bearing surfaces, at least one of which contains a metal selected from the group consisting of cadmium, silver, copper, lead and nickel, a film of a mineral lubricating oil within the motor oil viscosity range which produces an effective lubricating action but which would normally tend to corrode the said bearing surfaces, and maintaining the effectiveness of said lubricating oil film while materially inhibiting the 'corrosiveness of the same to said bearing surfaces by incorporating in the said lubricating oil about 0.01-2.0% by weight of an inhibiting material which consists primarily of a tri-alicyclic ester of phosphorous acid'in which the alicyclic radicals are selected from the group consisting of cyclohexyl and alkyl, aryl and aralkyl substituted cyclohexyl.

2. The method according to claim 1, in which the inhibiting material consists primarily of tricyclohexyl phosphite.

3. The method according to claim 1 in which the inhibiting material consists primarily of a trimethyl-cyclohexyl phosphite.

4. A motor oil for lubricating the bearings and cylinders of an internal combustion engine comprising a mineral lubricating oil within the motor oil viscosity range containing about 0.01-2.0% by weight of a bearing corrosion inhibiting material which consists primarily of a tri-alicyclic ester of phosphorous acid in which the alicyclic radicals are selected from the group consisting of cyclohexyl and alkyl, aryl and aralkyl substituted cyclohexyl.

5. A motor oil according to claim 4, in which the bearing corrosion inhibiting material consists primarily of tri-cyclohexyl phosphite.

6. A motor oil according to claim 4, in which the bearing corrosion inhibiting material consists primarily of a tri-methylcyclohexyl phosphite.

7. An improved lubricating oil comprising a mineral lubricating oil containing about 0.01- 2.0% of an additive which consists primarily of a tri-alicyclic ester of phosphorous acid in which the alicyclic radicals are selected from the group consisting of cyclohexyl and alkyl, aryl and arallryl substituted cyclohexyl.

HARRY V. ASHBURN. ROBERT E. CONARY. PAUL S. STUTSMAN. 

